This invention relates to the reproduction of a digitally encoded signal from a disk medium and in particular to the recovery of data added subsequent to pressing.
The introduction of optically readable disks recorded with data or digitally compressed audio and video signals, offers the consumer access to very significantly sized data records or sound and picture quality virtually indistinguishable from the original material. However, the provision of such features and potential for near identical replication exemplify a need to protect or control dissemination of the material contained within the disk. In a digital versatile disk (DVD) specification titled DVD Specification for Read-Only Disc/part 1, Physical Specifications Version 1, appendix K, a method is detailed which facilitates the individual identification of disks following mass production by use of a burst cutting area code. Disks may be identified by a series of radially positioned cuts or surface reflectance deformations which occupy a specified circumferential band adjacent to a specified disk clamping area. These radial stripes are positioned to over-write and partially obliterate a disk area specified for lead-in data. The BCA data can represent from 10 to 188 bytes of data which is modulated by phase encoding prior to over-writing. The BCA data comprises a data field, error detection and correction codes and pre and post amble fields.
When disk replay is initiated the lead-in data area is read and the lead-in data examined to determine the status of bit 16, which if set to 1 indicates the presence of encoded burst cutting area data. If BCA data is indicated, the burst cutting area is read and the data recovered. Current BCA data acquisition methods employ a serial process of data acquisition and error correction where erroneous data initiates a request for additional BCA data from the disk. This request usually jumps the transducer to the beginning of the lead in area then back to the nominal center of the burst cutting area in for a second attempt at BCA data recovery. Failure to recover this disk specific data may render further reproduction of the disk impossible. Such BCA data recovery failures may be attributed to poor data signal recovery possibly resulting from dirty BCA data or xe2x80x9ccuttingxe2x80x9d deficiencies, splattered disk material, swarf or inconsistencies of the lowered reflectance stripes representing the BCA data
An inventive method allows a disk replay system to acquire, detect and error-correct burst cutting area data more efficiently and effectively. A first method for acquiring data from a recording on a disk medium, comprises the steps of, successively reading bits defining a data set from different parts of the disk, continuously error correcting the bits to validate at least a part of the data set read from the disk, and, terminating reading upon successful validation of the data set by the error correcting step. A second method for acquiring data from a recording on a disk medium, comprises the steps of reading a data set beginning from a first position on the data recording, reading the data set from a second position radially spaced in a first direction from the first position absent acquisition of an error free data set from the first position; and, reading the data set from a third position radially spaced in an opposite direction beyond the first position absent acquisition of an error free data set from the second position.